The present invention relates to a hydraulic circuit for traveling in which two hydraulic motors for driving the traveling wheels can be rotated by employing one hydraulic pump.
And in this hydraulic circuit, if anyone of the traveling wheel, for example, a traveling wheel 12, may float due to the rough road surface, the load exerting on the hydraulic motor 14 becoming quite small, almost all amount of the high pressure fluid discharged from the hydraulic pump 11 is supplied to the hydraulic motor 14, so that the traveling wheel 12 is skidding to make traveling impossible.
In this case, by switching the opening-closing valve 19 from an open to closed state, the flow passing areas of the bifurcate portions 16a, 16b are controlled by the flow dividing valve 17 in accordance with the loads applied on the hydraulic motors 14, 15, so that the high pressure fluid from the hydraulic pump 11 is supplied in equal amount to the hydraulic motors 14, 15 to continue the traveling.
In the related hydraulic circuit, the flow dividing valve 17 is used to supply an equal amount of high pressure fluid to the hydraulic motors 14, 15. However, since this flow dividing valve 17 produces a great pressure loss when the fluid passes through it, the hydraulic motors 14, 15 have the lower pressure applied. As a result, there is the problem that the rotational torque (traction force) is lower in the scene where a great traction force is required.
It is an object of this invention to provide a hydraulic circuit for traveling that can rotate two hydraulic motors with a great rotational torque and at almost equal speed, even if different loads are applied on both hydraulic motors.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
A preferred embodiment of the hydraulic circuit for traveling includes a hydraulic pump, two hydraulic motors for driving and rotating the traveling wheels and a pumping passage for supplying a high pressure fluid discharged from the hydraulic pump to the two hydraulic motors. The pumping passage includes one end connected to the hydraulic pump and is bifurcated such that other ends are connected to the hydraulic motors. Two rotation detectors detect the rotational speeds of the hydraulic motors, respectively. A detection controller detects whether or not any traveling wheel is skidding by comparing the rotational speeds detected by the rotation detectors. Two braking force applying members apply a braking force only to the hydraulic motor of the skidding traveling wheel on the basis of the result of detection from the detection controller. The braking force applying members are installed in each of the hydraulic motors.
In another aspect, a traction control system for a traveling vehicle of a preferred embodiment includes at least two traveling wheels driven by a single hydraulic pump through respective hydraulic motors. The traction control system includes rotation detectors for respectively detecting rotation speeds of the traveling wheels, a computer, connected to the rotation detectors, for comparing the rotational speeds of the traveling wheels and computer-controlled brake units respectively provided to the traveling wheels, and independently controlled by the computer.
In yet another aspect, a preferred brake system for a traveling vehicle having at least two traveling wheels driven by a single hydraulic pump through respective hydraulic motors includes a parking brake for applying braking force to both of the traveling wheels when the hydraulic pump is not driven or the hydraulic pump does not provide sufficient hydraulic pressure to the hydraulic motors and an auxiliary brake for applying braking force to only one of the traveling wheels independently of the parking brake.
For example, suppose that one traveling wheel floats from the road surface, and one hydraulic motor for driving the traveling wheel has a quite small load. In such a case, the high pressure fluid from the hydraulic pump is substantially supplied to one hydraulic motor, so that one hydraulic motor is rotating (skidding) at high speed and the other hydraulic motor hardly rotates. Herein, the rotational speeds of the hydraulic motors are detected by the rotation detector, respectively, and the results of detection are output to detection controller. At this time, the detection controller detects that one traveling wheel is skidding by comparing the results of detection.
In this way, if one traveling wheel is detected to be skidding, the detection controller activates one braking force applying member to apply a braking force to one hydraulic motor alone, and balance the load of one hydraulic motor with that of the other hydraulic motor. Thereby, the high pressure fluid is also supplied to the other hydraulic motor, which is then rotated to continue the traveling. And if the other hydraulic motor is rotated, all the fluid discharge from the hydraulic pump is not supplied to one hydraulic motor, whereby it is possible to prevent one hydraulic motor from being damaged due to over speed.
Since there is no need of employing the flow dividing valve to release the skidding, the high pressure fluid supplied to both hydraulic motors produces less pressure loss, so that both hydraulic motors can be easily rotated with a great rotational torque and at almost equal speed.
Also, the braking force can be applied to the hydraulic motors in a simple constitution.
Further, the negative brakes installed in the hydraulic motors can be directly employed to apply the braking force to the traveling wheels that are skidding.
Also, the braking force applied to the hydraulic motors can be easily controlled.
Moreover, even if there is a difference in rotational speed between both hydraulic motors at the time of turning, it is possible to prevent the false recognition that the traveling wheel is skidding.
The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2000-302642 (filed on Oct. 2, 2000), which is expressly incorporated herein by reference in its entirety.